It is not too much to say that one who harbours impure or evil thoughts thereby spreads moral contagion among his fellow men. Bearing in mind that large numbers of people have within them latent germs of evil, germs which may never bear fruit unless some force from without plays upon them and stirs them into activity, the thought-wave sent out by an impure or unholy thought may be the very factor which awakens a germ into activity and causes it to begin to grow. Hence such a thought may start some soul upon a downward career. This man may in a similar manner affect many others, and so the evil spreads and ramifies in countless directions. Much harm is constantly done in this way; and although it may be done unconsciously, yet the perpetrator of the evil is karmically responsible for what he has done.
It is of course equally true, that a beneficent thought may affect others for good in a similar manner. Hence a man who realises this, may set himself to work to be a veritable sun, constantly radiating upon all his friends and neighbours thoughts of love, calm, peace etc. Very few realise how great a force for good they may thus wield, if they choose, through the power of thought. It often happens that a man is unable to help another man physically; in fact, the physical presence of the would be helper may be even distasteful to the sufferer; his physical brain may be closed to suggestions by prejudice or by religious bigotry. But his astral and mental bodies are far more easily impressible than the physical, and it is always possible to approach these by a wave, of helpful thought, affection, soothing feeling, and so on.
There are many cases where the best will in the world can do nothing physically; but there is no conceivable case in which either in the mental or astral world some relief cannot be given by steady, concentrated, loving thought. It should be noted that a thought-wave does not convey a definite complete idea, but rather tends to produce a thought of the same character as itself. Thus, for example, if the thought be one of devotion, its vibrations will excite devotion; but the object of the worship may be different in the case of each person upon whose mental body the thought-wave impinges.
***From Arthur E. Powell – The Mental Body